The body sheds dangerous heat by sweating and pushing blood to the skin surface. At least six common drug classes interfere with one or both. Beta-blockers reduce skin blood flow. Diuretics deplete fluid volume. Anticholinergics, in allergy pills and bladder medications, suppress sweating directly. None of these effects pause at sunset. When overnight temperatures no longer drop enough for the body to reset, each day's heat carries forward.
Among adults 65 and older, 54% take four or more prescriptions. A Medicare study found these drugs raised heat-hospitalization risk all summer, not only during declared heat waves. A 2026 scoping review estimated 40% of older adults' heat hospitalizations for dehydration were potentially preventable with timely medication adjustment. Diuretics and beta-blockers still carry no FDA heat warnings.
Don't stop taking anything. Do ask your prescriber whether your current regimen was designed for the summers you're living through now.
Beta-blockers (metoprolol, propranolol): Reduce skin blood flow; decrease sweating
Diuretics (furosemide, HCTZ): Deplete fluid volume; blunt thirst
Anticholinergics (diphenhydramine, bladder meds): Block sweating directly
Antipsychotics (quetiapine, olanzapine): Impair central temperature regulation
SSRIs (sertraline, fluoxetine): Increase sweating, accelerating dehydration
Tricyclics (amitriptyline): Decrease sweating; lower blood pressure
ACE inhibitor + diuretic: CDC flags this combination as significantly elevated risk
Evidence varies by class: Controlled trial data is strongest for anticholinergics and non-selective beta-blockers. For other classes, the case rests on epidemiological association and biological plausibility rather than randomized trials.
Questions worth raising with your prescriber:
- Which of my medications affect heat tolerance?
- Should dosing or timing change during extreme heat?
- Do any of my drugs combine to raise risk?